In the past, nippers with an open biasing function have been offered in which the opening-closing tool is two half-bodies with a cross-over pivot that have handle parts at the proximal ends and cutting parts at the distal ends, with an urging body provided between the half-bodies that urges the two handle parts open. This biasing body is a coil spring that spans between predetermined positions on opposing inner surfaces of the two half-bodies.
Consequently, with nippers having this open-biasing function, simply removing force that is applied to the two handle parts allows the two blades at the distal end parts to open due to the open-biasing of the biasing body. Therefore, opening and closing of the two blade parts can be promptly repeated by an operation in which the two handle parts are gripped firmly and loosely in succession, which is extremely convenient.
However, with nippers having this open-biasing function, the two handle parts cannot be opened more than is necessary, and when the two handle parts are mistakenly opened more than is necessary, problems will occur such as the attachment portion for the half-body will come off, or the biasing body will elongate and break.
Thus, as described in Japanese Unexamined Patent Application Publication No. Sho 61-130159, a nipper has been offered in which an open-biasing structure is provided in which one end part of the biasing body is attached only to one of the half-bodies, and the other end part is made to abut the other half body. With this structure, the problems described above are resolved, but from the standpoint of practical use, there are problems with use if the two handle parts are free to open excessively. In this regard, providing a stopper on the tool may be considered in order to prevent excessive opening of the two handle parts, but this is not realistic because mass production will suffer, causing an increase in cost.
The applicant of this invention has therefore offered an opening-closing tool (referred to below as “conventional example”) in Japanese Patent Publication No. 5289513 which resolves the problems described above.
This conventional example has a structure in which a first half-body having a first operating part on the distal end and a first handle part on the proximal end and a second half-body having a second operating part on the distal end and a second handle part on the proximal end have a cross-over pivot, and a biasing body that abuts the second half-body and provides an open bias on the two handle parts is provided on the first half-body. This structure has a configuration in which a recess for latching a distal end part of the biasing body is provided on the second half-body so that, as a result of latching of the biasing body and the recess, the two handle parts are biased open up to a predetermined open position, and, along therewith, opening of the two handle parts is prevented at this predetermined open position. When the two handle parts are additionally opened at a predetermined force from this predetermined open position, the distal end part of the biasing body separates from the recess.
Consequently, with the conventional example, the opening-closing operation is promptly carried out by the open-biasing mechanism, and a recess that latches the distal end part of the biasing body is provided; therefore, excessive opening of the two handle parts is prevented, greatly facilitating use. Moreover, because the distal end part of the biasing body is released from the recess, breakage of the biasing body can be prevented, to as great an extent as possible.